Endothelin-induced cyclooxygenase-dependent superoxide generation contributes to K+ channel functional impairment after brain injury

This study determined if endothelin (ET-1) generates superoxide anion (O-2(-)) in a cyclooxygenase-dependent manner and if such production contributes to impairment of dilation to activators of ATP-sensitive K+ (K-ATP) and calcium-sensitive K+ (K-ATP) channels following fluid percussion brain injury (FPI) in newborn pigs equipped with closed cranial windows. Superoxide dismutase (SOD)-inhibitable nitroblue tetrazolium (NBT) reduction was determined as an index Of O-2(-) generation. Under non-brain injury conditions, topical ET-1 (10(-10) M, the concentration present in CSF following FPI) increased SOD-inhibitable NBT reduction from 1 +/- 1 to 17 +/- 3 pmol/mm(2). Indomethacin, a cyclooxygenase inhibitor, blunted such NBT reduction (1 +/- 1 to 4 +/- 1 pmol/mm(2)), while the ET-1 antagonist BQ123 blocked NBT reduction. BQ123 and indomethacin also blunted the NBT reduction observed after FPI. Under non-brain injury conditions, ET-1 (10(-10) M) coadministered with the K-ATP and K-ca channel agonists cromakalim and NS1619 (10(-8), 10(-6) M) diminished dilation to these K+ channel agonists, while indomethacin partially prevented such impairment (13 +/- 1 and 23 +/- 1 vs. 2 +/- 1 and 6 +/- 1 vs. 6 +/- 1 and 14 +/- 2% for cromakalim in untreated, ET-1, and ET-1 plus indomethacin-treated piglets, respectively). Cromakalim- and NS1619-induced pial artery dilation was attenuated following FPI, while indomethacin or BQ123 preadministration partially prevented such impairment (13 +/- 1 and 23 +/- 1, sham control; 1 +/- 1 and 4 +/- 1, FPI; 8 +/- 1 and 16 +/- 3%, FPI and indomethacin-pretreated for responses to cromakalim 10(-8), 10(-6) M, respectively). These data show that ET-1 increased O-2(-) production in a cyclooxygenase-dependent manner and contributed to this production after FPI. These data also show that ET-1 blunted K-ATP and K-ca channel-mediated cerebrovasodilation in a cyclooxygenase dependent manner. These data suggest that ET-1-induced cyclooxygenase-dependent O-2(-) generation contributes to K-ATP and K-ca channel function impairment after FPI.